For imparting softness and smoothness to fibers, wax, oils or fats such as fatty acids and quaternary ammonium salts containing long chain alkyl groups were widely used in the past. Certain organopolysiloxanes are also known as fiber treating agents. For the purposes of improving water repellency, softness, smoothness, resiliency, and the like, there were proposed dimethylpolysiloxanes, epoxy-containing polysiloxanes and amino-containing polysiloxanes (see Japanese Patent Publication Nos. 1480/1973 and 43617/1979).
Fats, oils and quaternary ammonium salts fail to provide satisfactory softness. Dimethylpolysiloxanes can impart smoothness, but are less satisfactory in softness. Epoxy-containing polysiloxanes can impart fairly good smoothness and softness, but to a less extent than can amino-containing polysiloxanes.
The amino-containing polysiloxanes can impart fully satisfactory softness and smoothness to fabrics, but suffer from a tarnish phenomenon. Oxidation of amino groups can occur under the influence of UV radiation or the like during heat treatment involved in the fiber treatment process or storage of treated fabrics, giving rise to discoloration and especially, yellowing in the case of white or light color fabrics.
For the purpose of overcoming the yellowing problem, a variety of proposals have been made, for example, amidization of amino groups with acid anhydrides or acid chlorides (Japanese Patent Application Kokai No. 101076/1982) and blocking of active hydrogen of amino groups with epoxy compounds (Japanese Patent Publication No. 44073/1987). These methods achieve some improvement in yellowing as compared with the use of amino-containing polysiloxanes, but to a still unsatisfactory extent. Another drawback of these methods is a loss of softness.
Moreover, the treatment with amino-containing polysiloxanes renders fabrics water repellent. Natural fiber fabrics which are hydrophilic by nature would undesirably lose their own property when treated therewith.
For imparting hydrophilic nature to fibers, it is known to treat fibers with polyether group-containing siloxanes. However, this treatment provides noticeably inferior softness as compared with the use of amino-containing polysiloxanes.
There is a need for a fiber treating composition providing a good compromise among softness, hydrophilic property and anti-yellowing.